Let the length of the room be l m.
Given:
Breadth of the room = 10 m
Height of the room = 4 m
Area of the four walls = [2(l + b)h] sq units.
= 168 m2
∴ 168 = [2(l + 10) 4]
⇒ 168 = [8l + 80]
⇒ 168 - 80 = 8l
⇒ 88 = 8l
⇒ l = m = 11 m
∴ Length of the room = 11 m